Movements are produced by neural circuits in the spinal cord and hindbrain. The proposed work will explore basic design principles of the neural networks in the hindbrain as a foundation for understanding their disruption in injury and disease. Pilot data from the zebrafish model indicate that hindbrain networks might be built via some simple initial principles that relate stripes of transcription factor expression to the position, age, morphology, projections, and functional properties of neurons. The specific aims will test these principles by asking: 1) Is there a relationship in hindbrain between age and morphology within neurons in a given transcription factor stripe? This aim will use transgenic approaches and single cell labeling to determine the morphological properties of neurons in a specific transcription factor stripe to assess how they vary with respect to their time of differentiation. 2) Are there orderly patterns of connectivity between neurons in different stripes? This aim will ask if there are topographically ordered projections between stripes in the hindbrain. Neuronal connections will be examined by patch recording from one cell, while testing inputs from another stripe expressing the light-activated protein channelrhodopsin (ChR2). 3) How does the morphology, connectivity, and position of neurons within stripes change as the animal matures? This final aim examines if age related topographic connections established early on in development persist into later stages. This can be achieved via labeling of cells with membrane tagged proteins or dyes followed by tracking them over long time periods to examine their movements and the stability of their projections.